Poly-ynes

Diynes and triynes refer to alkynes containing two or three triple bonds poly-ynes contain multiple triple bonds. A conjugated triyne is a straight-chain hydrocarbon with triple bonds alternating with single bonds. An examples is... 

Another, simple form of elemental carbon would be chains formed from carbon atoms. As a prototype model a single>stranded chain is most suitable. If branching were to be considered, all intermediate forms up to and including the diamond and graphite like clusters would be included. For non branched chains, the two variants to choose from are a system of alternating singly and triply bonded carbon atoms (poly-ynes), and a system with all double bonds (cumulenes). Cumulene structures are assumed to be the preferred ones for odd membered chains, whereas the even ones may have some poly-yne character. Recent studies on linear Cg show that a cumulene-like structure is preferred, both at the SCF level and when correlation is accounted for(50). 

We have chosen the C20 poly-yne ring as a reasonable representative for a large chain molecule. The bond lengths optimized at the Hartree-Fock level are 1.37 A and 1.20 A, respectively. The same values are found for the experimental bond lengths in 1,3-buta-di-yne CHg-C C-C C-H, indicating that there is very little n conjugation in the system. 

The cohesive energy per carbon atom in a poly-yne ring is only 99.1 kcal/mol, clearly lower than the value in Cc. Anticipating a long and complicated route of formation when starting from graphite, in does not seem likely that any of the larger clusters observed experimentally would have a linear or cyclic chain structure. 

Metal-acetylide complexes have been used as a unit of organometallic polymers that have metallic species in the main chain [20]. Representative examples are metal-poly(yne) polymers (19) of group 10 metals depicted in Scheme 5. These polymers are easily prepared from M(PR3)2Cl2 (M=Pt, Pd) and dialkynyl compounds catalyzed by Cu(I) salts in amine. Recently, this synthetic method was successfully applied to the construction of metal-acetylide dendrimers. 

Metal-acetylide complexes including metal-poly(yne) polymers often show unique properties [21-23]. Thus, metal-acetylide dendrimers are of interest because amplification of the functionality due to metal-acetylide units based on three-dimensional assembly with a regular dendritic structure is expected. 

Scheme 1. Chemical Structures of some important linear n-conjugated polymers. Polyenes 1, poly-ynes 2, polyenynes 3, poly(p-phenylene)s (PPP) 4, polyphenylenevinylenes (PPV) 5, polyphenyleneethynylenes (PPE) 6.

The preparation of poly-ynes from diiodoacetylene has recently been carried out in the presence of Ni/dppe complexes (Eq. 4) [39] ... 

Shibata further examined consecutive reactions of poly-ynes. When tetraynes (where two 1,6-diyne moieties were connected with a naphthalene spacer) were submitted, quinquearyl compounds with four consecutive axial chiralities were obtained (Scheme 11.15). Even an octayne proved to be a good substrate, and a noviaryl compound with eight consecutive axial chiralities was obtained in almost perfect enantioselectivity (Scheme 11.16) [23]. 

IV. Metal Cluster Complexes Derived from 1,3-Diynes or Poly-ynes. 130... 

VIII. Formation of Free Di- and Poly-ynes by Reactions at Metal Centers. 224... 

Transition Metal Chemistry of 1,3-Diynes, Poly-ynes, and Related Compounds 73... 

The presence of multiple C C moieties in di- and poly-ynes hints at a vast potential for expansion of this chemistry. Recent developments in the chemistry and material properties of these complexes have led to a surge of interest in the chemistry of these highly unsaturated ligands. Some of these results have been the subject of several recent short reviews and highlight articles. 

The presence of multiple C=C moieties affords the potential to assemble novel arrays of metal centers by combinations of a- and tt-bonding interactions. " However, examples of multimetallic complexes containing poly-yne and poly-yndiyl ligands are limited, although preliminary reports suggest that there is much scope for the preparation of new structural types. 

Group 14 reagents are widely used in preparative organic poly-ynyl chemistry. Typical examples include the use of trialkylsilyl moieties as protecting and stabilizing groups in poly-yne synthesis while tetravalent tin reagents have proven to be of remarkable utility in the construction of carbon—carbon bonds. ... 

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